It is known that in solid-state image pickup apparatuses, for example, CCD image sensors and CMOS image sensors, crystal defects in a photodiode that is a photoelectric conversion element of a light receiving unit and the interface state density at the interface between the light receiving unit and an insulating film thereupon are sources of dark current.
Out of such, an embedded photodiode construction is effective as a method of suppressing generation of dark current caused by the interface state density.
An embedded photodiode is configured for example by forming an n type semiconductor region and forming a p type semiconductor region (hole accumulation region) for suppressing dark current that is shallow and has a high concentration of dopant on the surface of such n type semiconductor region, that is, near the interface with an insulating film.
As the method of fabricating such embedded photodiode, it is typical to carry out ion implantation of B or BF2 as a p type dopant and then an annealing process to fabricate a p-type semiconductor region near the interface between the n type semiconductor region that constructs the photodiode and the insulating film.
Also, in a CMOS image sensor, the respective pixels are formed so as to include a photodiode and various transistors such as read, reset and amplifier transistors. A signal that has been photoelectrically converted by the photodiode is processed by such transistors. A wiring layer including metal wires on multiple layers is formed on top of the respective pixels. A color filter that restricts the wavelength of light incident on the photodiode and/or an onchip lens that focuses light on the photodiode are formed above the wiring layer.
Device constructions with a variety of characteristics have been proposed as CMOS image sensors.
More specifically, CMD (Charge Modulation Devices; see Patent Literature 1, 2, and 3) that use CCD-like features in their photoelectric conversion element constructions and BCDM (Bulk Charge Modulation Devices; see Patent Literature 4) have been proposed.
In addition, FWA (Floating Well Amplifiers; see Patent Literature 5 and 6) have been proposed. With a FWA, a channel is formed in the surface in accordance with the amount of charge of photoholes accumulated to local maxima, with the source-drain current changing according to the amount of charge at the surface, resulting in the ability to read in accordance with the signal charge.
In addition, a variety of devices have been proposed, such as a threshold modulation image sensor (VMIS: Vth Modulation Image Sensor, see Patent Literature 7, 8, 9, and 10) where the light receiving unit and the signal detecting unit are split and disposed adjacently.
Also, the solid-state image pickup element described below was proposed in Patent Literature 11.
This solid-state image pickup element includes a light receiving element that functions so as to carry out photoelectric conversion of incident light, accumulate the signal charge obtained by such photoelectric conversion, and output a signal voltage in accordance with the amount of accumulated signal charge. This light receiving element has a potential distribution whereby it is easy for signal charge to accumulate at the same position when viewed as a plane and flow of a surface channel current is facilitated.
Such CMOS image sensors are frontside illumination solid state image pickup apparatuses where light is fundamentally incident from the front side of the device.
On the other hand, a backside (rear surface) illumination solid state image pickup apparatus that is made thinner by grinding the back side of a silicon substrate on which photodiodes and a variety of transistors have been formed and carries out photoelectric conversion of light incident from the back side of the substrate has been proposed (see Patent Literature 12).